This invention relates to turbomachines, in general; and, in particular to a method and apparatus for testing portions of a turbomachine material after the turbomachine has been in service for a predetermined interval of time.
In recent years, turbomachines such as gas turbines have been developed to provide increased output at higher firing temperatures. This increased duty requirement has promoted the use of high temperature alloys in large rotor forgings. The expected life of a turbomachine rotor may extend over periods in excess of twenty-five years during which time properties in such rotor material can be expected to degrade which could impair the availability of the turbine rotor for cyclic duty. The ability of a gas turbine to track load demand and therefore be subject to multiple start-ups and shutdowns (cyclic duty) is a distinct advantage of a gas turbine. It is important therefore to be able to confirm the actual condition of a turbomachine part such as a turbine rotor over various times during the operating life of the turbomachine.
Concern over material degradation over time is an important factor in the specification of turbine rotor alloys. This concern has led to the choice of more exotic alloys at a substantially increased cost in order to assure the continued reliability of the rotor material. If there were a way to inspect a rotor so that the actual condition of a forging material could be tested without destroying the turbomachine part, then a substantial saving in the choice of rotor material as well as a better informed decision regarding its continued operation could be made. In addition, exotic alloys are difficult to forge in large sizes and machining is difficult due to the material's high strength.